'Bosnia', a commentator noted as he watched the Foreign Secretary agonise at the height of the Balkan wars, 'will be on Douglas Hurd's tombstone.' Lord Hurd is still with us, but tens of thousands of Bosnians are dead.

The connection between the grave statesman and the graves of the slaughtered is Brendan Simms's theme. We may see better demolitions of the last Tory government when the official records are released, but Simms's attention to telling detail and cool, literate anger make Unfinest Hour the best epitaph for the wretched years of the Major administration I've read to date. His argument, that what Britain did to Bosnia stands alongside Munich and Suez as a great Conservative foreign policy disaster, is irrefutable.

The wars of the former Yugoslavia had one cause: irredentist Serbs, who combined nationalism and socialism in a faintly familiar mixture. They didn't merely want power, but to guarantee that only Serbs lived in Serb-occupied territory. Thus, while the Bosnian government retained Serb and Croat backing, every mosque in the lands Milosevic's supporters held was levelled.

For years, Britain led the chant that nothing could be done. Yet in the assaults that forced Milosevic to sign the Dayton Agreement of 1995 and in the Kosovo campaign, the determined application of force compelled the supposedly mighty Serb armies to back off and precipitated a democratic revolution in Belgrade.

Simms mints the phrase 'conservative pessimism' to describe the mentality of Hurd, Malcolm Rifkind and David Owen. They evaded Serb responsibility for the atrocities and vastly overestimated the difficulties of intervention. Exhausted by Ireland and haunted by Suez and Vietnam, Conservative politicians and the 'experts' in the press and think-tanks maintained that ethnic cleansing was an unpleasant fact of life.

The dominant ideology might have propelled Britain to sit out the Bosnian conflict. But Hurd went further. Not only did Britain refuse to reverse Serb aggression, 'we' made damn sure no one else did either.

'Pessimism' doesn't quite capture the malice of British policy. American attempts to lift the arms embargo on the Bosnian government were opposed by vehement mandarins. No-fly zones, relief for Bosnian enclaves, war-crimes tribunals and armed protection for humanitarian convoys were fought to the last ditches of the European Union and United Nations. 'Any time there was a likelihood of effective action,' said Tadeusz Mazowiecki, the Polish Prime Minister, '[Hurd] intervened to prevent it.'

Post-imperial weariness mixed with genuine imperial arrogance. No one would make Britain lose face by forcing the Foreign Office to think again, particularly not the 'naïve' Americans. Throughout the war, the British conservatives were resentful Greeks to wide-eyed American Romans.

The conviction that Britain had a superior knowledge of the futility of reforming a wicked world pushed Whitehall into a kind of madness. Only the possession of an unhinged mind can explain how Malcolm Rifkind, a Defence Secretary who had never seen combat, could bellow 'you Americans don't know the horrors of war' at Senator Bob Dole, who lost an arm in World War II. 'Your guys were usually so refined,' an American diplomat said of the Washington Embassy. 'But they were going crazy on this.'

Rifkind's ravings - Senator John McCain came close to slapping him at one meeting - will surprise readers in a Britain where snobbery gives an unwarranted benefit of the doubt to patrician conservatives.

The politicians who dealt with Bosnia were gentlemen of moderate temperament; sophisticates with breeding and manners, who were a cut above the rabble-rousing Thatcherites. Yet Hurd out-Thatchered Thatcher, who honourably opposed Serb aggression, when he declared that 'there is no such thing as the international community'.

He then sank to a depth I can't remember Thatch reaching when he effectively closed Britain's borders to Bosnian refugees. 'The civilians have an effect on the combatants,' he explained. 'Their interests put pressure on the warring factions to treat for peace.' You have to read this disgraceful passage several times before you realise that Hurd was denying sanctuary to the victims of the Serbs (and of his diplomacy) so he could use their misery to force Bosnia to cut a deal with the ethnic cleansers.

Corrupt language followed corrupting policies. Simms is very good on how the distinction between aggressors and victims was blurred and everyone became a member of a 'warring faction' filled with 'ancient hatreds'; on how the secular Bosnian government was transformed into 'the Muslims'. The Bosnian war, he writes, 'became a strange beast: a perpetratorless crime in which all were victims and all more or less equally guilty'. The debasement of the terms in which Britain could think about the Balkans reached a nadir when Kirsty Wark described a Catholic Croat Bosnian spokesman as a 'Muslim' on Newsnight and ignored his protestations that he was nothing of the sort.

Ah, but it takes you back. David Owen Balkanising the Balkans. Major complaining about critics 'grandstanding from the safety of their armchairs'. (Try it at home if you believe it is possible.) Douglas Hogg screaming that it would take 500,000 troops to turn back the Serbs. MI6 spinning that the Bosnians were massacring themselves. And - how could we forget? - the valiant General Sir Michael Rose, who, while refusing to contemplate effective military action by the troops under his command, opined that demands for intervention came from 'the powerful Jewish lobby behind the Bosnian state' and wondered at a performance of Mozart's Requiem in Sarajevo if Alija Izetbegovic, the cultured Bosnian president, understood 'the Christian sentiment behind the words and music'.

Rose's 'ancient hatreds' coexisted with a grudging admiration for Serb officers. Even the butcher of Srebrenica, General Ratko Mladic, wasn't all bad, in his considered view, but a 'man who generally kept his word'.

Unfinest Hour is more than a diplomatic history. It is a grim cultural study of the political, military and intellectual élites of the early Nineties who watched suffering with a faux-realist relish and saw humane treatment as more dangerous than the disease.

Formal differences between Left and Right scarcely mattered. Hurd sounded like John Pilger when he implied it was racist to intervene in Bosnia but not in Angola or Cambodia. Pilger mimicked Hurd when he accused the Americans of wanting to 'recolonise' the Balkans. For every Lord Carrington harrumphing that 'they were all as bad as each other' there was a Misha Glenny saying that those ancient 'irrational beliefs' drove all parties in the Balkans into cycles of insane slaughter.

Kosovo supplies Simms with a happy ending of sorts. If he could find the time, Tony Blair would enjoy this dissection of the experts who now oppose the Afghan war. But just as Northern Ireland blinded Hurd to what was before his nose in the Balkans so, I fear, the success of Kosovo blinds supporters of the campaign against bin Laden to its huge dangers.